The invention relates to an integrated dynamic semiconductor memory having a matrix-like memory cell array containing memory cells which are combined to form units of column lines and row lines. A read access to one of the memory cells is time controlled from a selection of one of the column lines to an evaluation with a sense amplifier.
Integrated dynamic semiconductor memories have memory cells which are frequently provided in a matrix-like memory cell array. The memory cells are usually combined to form addressable units of column lines and row lines. These may, for example, be bit lines and word lines. The memory cells may be provided at points of intersection of the bit lines and word lines.
During read access to one of the memory cells, the relevant row line and column line are generally selected through the use of a decoder. After selection of the relevant row line, data signals from the memory cells along the row line are present on the corresponding column lines. These data signals are amplified in an adjacent so-called sense amplifier strip in the memory cell array. After selection of the relevant column line, the data signal from the addressed memory cell is released for further processing in a further sense amplifier (also called secondary sense amplifier). To prevent the further sense amplifier from switching too early, which may sometimes result in incorrect evaluation by the sense amplifier, it is necessary to wait for the time required until the already amplified data signal is present at the further sense amplifier.
The decoder for selecting one of the column lines and the further sense amplifier for further processing the data signal which is to be read are usually provided at the edge of the memory cell array. The maximum time to be waited between selection of the column line and evaluation by the further sense amplifier is accordingly measured from the delay time for the selection signal for selecting the column line to the most distant sense amplifier strip and from the return time for the amplified data signal on the relevant data signal line.
This control with respect to time may be achieved by using a delay circuit, for example, which models the maximum delay time for the selection signal and the maximum delay time for a data signal. Such a delay circuit has, by way of example, an inverter chain or, generally, delay stages constructed from logic gates. By modeling delay times in this way, there is a general reduction in the robustness of the integrated circuit, however. Such delay elements are comparatively sensitive to process, temperature and voltage fluctuations. This may result in variable and/or imprecisely adjustable delay times for the delay circuit. As a result, the operability of the relevant circuit configuration may be impaired during read access.
It is accordingly an object of the invention to provide a circuit configuration for an integrated dynamic semiconductor memory for performing a read access, from a selection of one of the column lines to an evaluation by a sense amplifier, which overcomes the above-mentioned disadvantages of the heretofore-known circuit configurations of this general type and in which the operability of the circuit is ensured over a broad range of process, temperature and voltage fluctuations.
With the foregoing and other objects in view there is provided, in accordance with the invention, an integrated dynamic semiconductor memory, including:
a memory cell array configured as a matrix and including memory cells; column lines and row lines;
the memory cells being combined to form addressable units with the column lines and the row lines;
a selection signal line running across the memory cell array for transmitting a selection signal for selecting one of the column lines;
a decoder connected to the selection signal line;
a sense amplifier having an input, the sense amplifier being jointly allocated to all of given ones of the memory cells provided in a selected one of the column lines;
a data signal line for transmitting a data signal of one of the memory cells present on the selected one of the column lines across the memory cell array, the data signal being an amplified data signal;
the input of the sense amplifier being connected to the data signal line for further processing the data signal; and
the memory cell array having an edge and having opposite sides, the decoder and the sense amplifier being disposed at the edge and respectively on the opposite sides of the memory cell array.
In other words, the integrated dynamic semiconductor memory according to the invention has memory cells which are provided in a matrix-like memory cell array and are combined to form addressable units of column lines and row lines. It also has a decoder for selecting one of the column lines, the decoder being connected to a selection signal line for the purpose of transmitting a selection signal, and a sense amplifier which is jointly allocated to all of the memory cells in a selected column line. A data signal line is used to transmit an already amplified data signal from a memory cell in the selected column line, the data signal line being connected to the input of the sense amplifier for the purpose of processing the data signal further. The decoder for selecting one of the column lines and the sense amplifier are provided at the edge and on opposite sides of the memory cell array. This means that by isolating or separating the control for selection of the column lines and of the data output path, a kind of domino effect can be utilized during the control. This means that successive process steps in the process of a read access are controlled by the respective preceding signal. The process of the read access is thus provided with a self-adjusting manner of operation.
The active selection signal, which runs on the selection signal line via the memory cell array, selects the relevant column line, which releases the addressed memory cell""s data signal for the purpose of transmission on the data signal line. The transmitted data signal, like the selection signal, runs toward the sense amplifier and reaches it at virtually the same time as the selection signal. During such a read access, the influence of technology on the signal delay time can thus be taken into account on a self-controlling basis. This eliminates modeling of the signal delay times through the use of delay elements, which prevents susceptibility to process, temperature or voltage fluctuations.
As soon as the data signal has reached the sense amplifier, it can be amplified by the sense amplifier and output for further processing. Since the data signal and the selection signal for selecting the column lines reach the sense amplifier at virtually the same time, the sense amplifier can be controlled by the selection signal for selecting the column lines in order to process the data signal further.
According to another feature of the invention, the semiconductor memory has memory cells, combined to form units of redundant column lines, and redundancy circuits for selecting one of the redundant column lines. In order to achieve the shortest possible signal paths, the redundancy circuits are usually provided next to the decoder for selecting one of the column lines. In the present case, the redundancy circuits are thus provided together with the decoder on the same side of the memory cell array.
If the semiconductor memory has a first and a second memory cell array which have the same structural configuration and are provided next to one another, then a sense amplifier provided between the first and second memory cell arrays can be allocated to the first and second memory cell arrays for the purpose of processing data signals further. Redundancy circuits usually have programmable fuses, e.g. in the form of laser fuses, which need to be accessible from the surface of the semiconductor memory. If there is a redundancy circuit between the first and second memory cell arrays, the sense amplifier cannot be allocated to the first and second memory cell arrays jointly, because the lines cannot be routed over the redundancy circuit. On the other hand, suitable routing of lines is possible as a result of providing the redundancy circuits together with the decoder on the side of the memory cell array opposite from the sense amplifier, according to a preferred feature of the invention. A sense amplifier allocated to the first and second memory cell arrays for the purpose of processing data signals further permits a saving in terms of surface area.
In a further embodiment of the invention, the semiconductor memory has a first and a second sense amplifier which are provided between the first and second memory cell arrays and are each allocated to one of the memory cell arrays for the purpose of processing data signals further. Each of the sense amplifiers has an output for outputting the respective data signal which is to be processed further. In the interests of a low space requirement, the outputs of the first and second sense amplifiers are connected to a common output signal line.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an integrated dynamic semiconductor memory with a time controlled read access, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.